The function of a storage warehouse is to store containers for long periods of time. Typically, a property owner packs property into a container and ships the container to the storage warehouse where the container is cataloged and stored in the warehouse until such time as the owner wishes to retrieve it.
To facilitate the storage of large numbers of containers, the storage warehouses employ rows of box shelving, or racks. A plurality of racks are aligned substantially parallel to one another and spaced so as to form file aisles between adjacent racks. A typical file aisle is approximately three feet wide. Each file aisle has an ingress and an egress. Thus, a worker can walk down a file aisle to shelve or unshelve a container. In an installation in which file aisles are very long, periodic breaks within a row of racks are employed. These periodic breaks form cross aisles. Thus, the layout of a typical storage warehouse comprises a matrix of racks.
Typically, each rack is several floors high and is divided into a plurality of levels. Typically, each level is 8-10 feet high, and each rack comprises 34 levels (although racks comprising up to eight levels are not uncommon). To enable a worker to access containers on an upper level, walkways are disposed in the file aisles between adjacent racks at every level. These walkways are essentially grates. Each file aisle has an ingress and an egress on each level.
Typically, large, existing warehouses are used for conversion into storage warehouses. Commonly, such existing warehouses are old and have high voltage electrical power input (e.g., 277 V). Some storage warehouses also have low voltage electrical power input (e.g., 120 V). Due to their large size, storage warehouses commonly use high intensity discharge (HID) lamps for lighting. Several problems are known to exist with this type of lighting system. HID lamps tend to become very hot in use and, consequently, present health and safety hazards. Also, HID lamps are basically point sources. Consequently, HID lamps radiate in a pattern such that the light is blocked by the grating of the walkways. One of the biggest drawbacks to using a lighting system based on HID lamps is that HID lamps are expensive to operate. Since HID lamps take a fairly long time to heat up and cool down, it has been observed that, in a storage warehouses employing a lighting system based on HID lamps, all the HID lamps in the storage warehouse are turned on at the beginning of the day, and burn constantly until the end of the day. Thus, HID lamps burn 100% of the day, in 100% of the storage warehouse. Since workers access only a relatively small portion of a storage warehouse at any given time, clearly a lighting system based on HID lamps is wasteful and expensive.
Several attempts have been made to develop lighting systems that use fluorescent light fixtures. These systems are improvements over the HID-based systems in that fluorescent light fixtures are cooler and, consequently, less hazardous. Fluorescent light fixtures are more efficient and, consequently, less expensive to operate. Additionally, fluorescent light fixtures are linear and, consequently, radiate more uniformly downward. Thus, less light is blocked by the grating of the walkways. However, it has been observed that lighting systems based on fluorescent light fixtures may still operate 100% of the day, in 100% of the storage warehouse.
To satisfy a need in the art for a storage warehouse lighting system that illuminates only the aisles within the warehouse that a worker is using, several attempts have been made to connect the fluorescent light fixtures to a timer system. It is known to install twist timers at each ingress and each egress of each level of each rack. However, it has been observed that warehouse lighting systems based on twist timers have several drawbacks as well. First, twist timers are expensive to install due to the sheer number of twist timers needed for a typical storage warehouse. Second, such a system is hazardous because twist timers require live high voltage in the racks. Third, high voltage lines must be run from the breaker panel, through conduits installed in the racks, to the timers, and back to the panel, thus adding considerable cost. Fourth, the ordinary use of twist timers in such an environment results in a considerable rate of breakage to the timers. Fifth, since the twist timers are located in the aisles, they can be overridden by anyone in the aisle. Finally, twist timer systems are not suitable for storage warehouses having 277 V high voltage input since commonly available twist timers do not operate using so high a voltage.
Warehouse lighting systems using motion detectors have also been attempted. However, it has been observed that the racks are too unstable for such a system. For example, a load of containers being brought into or out of the warehouse via a cross aisle frequently will shake the racks as it passes by, thus causing the motion detectors to illuminate a considerable number of file aisles that are not in use.
Thus, there is a need in the art for a low cost, energy efficient, tamper-resistant, low voltage storage warehouse lighting system that minimizes illumination of file aisles not being used.